<p>Particulate matter (PM) fluctuations in Malaysia present significant environmental and public health hazards. However, there remains a paucity of comparative studies examining short-term monsoon-induced variations between urban-commercial and suburban-coastal regions, particularly those utilising high-resolution hourly data to evaluate intra-seasonal co-variability of PM_2.5 and PM₁₀ across different monsoon regimes. This investigation seeks to address this gap by analysing hourly, daily, and seasonal fluctuations of PM_2.5 and PM₁₀ in Kuala Lumpur (KL), a central-peninsular urban hub, and Johor Bahru (JB), a southern coastal setting. The study highlights similarities and differences attributable to distinct emission profiles, urban densities, and meteorological influences during the Northeast Monsoon (NEM) and Southwest Monsoon (SWM) regimes. Data obtained from national Continuous Air Quality Monitoring stations were subjected to statistical analysis, MATLAB 2024b was utilised for temporal series processing, and Pearson’s correlation coefficient was used to determine the linear relationship and co-variability between particulate fractions. The HYSPLIT model was employed to simulate 24-hour atmospheric dispersion patterns to identify pollutant transport trajectories and source regions. Air quality conditions were evaluated using the Air Quality Index (AQI), PM concentrations ranged from “good” to “moderate” in JB, while reaching “unhealthy for sensitive groups” in KL. Notably, KL exhibited higher PM_2.5/PM₁₀ levels, increased variability, and more frequent short-term pollution episodes, predominantly during the SWM. Strong positive correlations between PM_2.5 and PM₁₀ at both locations (high R² values) suggest potential shared influences or emission sources, with each parameter serving as a dependable predictor of the other. HYSPLIT analyses further demonstrated the combined influence of local emissions and seasonal airflow, including the transport phenomena from urban to surrounding regions. In conclusion, this study provides compelling evidence that monsoonal dynamics and urban morphology collaboratively influence PM variability in Malaysian cities. These findings offer valuable insights for the development of targeted air quality management strategies and region-specific mitigation measures.</p> Graphical Abstract <p></p> <p>This graphical abstract provides an overview of this study, which investigates the temporal dynamics and source contributions to atmospheric PM₂.₅ and PM₁₀ in selected Malaysian urban areas affected by monsoonal circulation. The background summarises key aerosol processes, including transport, dispersion, and chemical mixing, and compares pollution characteristics between urban/commercial and urban/coastal zones. These comparisons help clarify population exposure to primary emission sources such as vehicles, industry, and maritime activities. Different methodologies employed to measure fluctuations in hourly particulate matter fractions across cities and time scales are visually depicted in the graphical abstract. Descriptive statistics summarise central tendencies and variability, using measures like the mean, standard deviation, standard error, and extreme values. MATLAB-based time-series analysis was utilised to reveal diurnal and seasonal patterns, while Pearson’s correlation coefficient assesses the strength and linearity of relationships between parameters, aiding source identification. The HYSPLIT model illustrates short to long-range airflow routes and potential transboundary pollution influences. Results from the time series show distinct diurnal peaks, especially in Kuala Lumpur, indicating intensified urban emissions, with Pearson correlation demonstrating a strong positive linear relationship between PM₂.₅ and PM₁₀ at each location, with coefficients of 0.97 and 0.83 in KL and JB, respectively. HYSPLIT simulations also indicate short-term atmospheric transport influenced by monsoon-driven wind patterns. Air-mass trajectory analyses reveal urban-regional airflow patterns affecting pollutant dispersion. The analyses further suggest shared emission sources influenced by urban activities, maritime operations, and seasonal airflow patterns. This also highlights the urban-rural transport of emissions, which represents environmental injustice to rural communities. Elevated particulate concentrations during morning and evening hours reflect emissions from road traffic. The graphical abstract presents an integrated view of local emissions, urban-rural airmass transport, and regional transport phenomena, offering valuable insights for air quality management and policy development in rapidly urbanising tropical regions.</p>